330 



ELSA SHADALL 



culture medium was avoided for a short time, such water is 

 less dense than the usual medium. Dilute salt solution induces 

 the avoiding reaction when Opalinas are transferred to it from 

 the rectum of a frog. 



If an iodin-green or methyl-green crystal is dropped into a 

 culture medium of Opalinas, they will respond by the avoiding 

 reactions (Fig. 2). In some instances, they collected around 



CULTURE 



Q 9 







■■■ ssQ,, 







-;■■.■ 



METHYL GREEN 



-o 







<±/h J 



o 







CULTURE 







METHTLENE BLUCy 



Fig. 2. — Showinp reactions to chemicals 



the crystals but, as they are very susceptible to these chemicals, 

 in a short time even comparatively dilute solutions caused 

 death. Peranema (Mast, '12) is apparently much more resistant 

 to the effect of iodin-green, methyl-green, and methyl-blue. 

 Opalina avoids methyl-orange and a .4% solution of methylene 

 blue (Fig. 2). If, by chance, it has ventured into these chemi- 

 cals, it will turn to the right without revolving or backing, and 

 find its way out. It was noted that some Opalinas which swam 



